Yesterday I was out with my running group, and chatting with an acquaintance. She was saying that someone at her office had accused her of “eating her feelings” when she was stressed.
Her: She accused me of eating my feelings! I’m kind of upset she would say that…so I had a cookie, and then a latte, and some Hershey Kisses, and…then I realized she was right.
Me: Then of COURSE you eat your feelings! Your feelings are DELICIOUS!
(Sci’s feelings. They are indeed delicious. Source)
And so, when Sci found this paper, she really almost gave a mad scientist laugh at the coincidence.
Ulrich-Lai, et al. “Pleasurable behaviors reduce stress via brain reward pathways.” PNAS, 2010.
Many scientists are interested in studying the potential causes behind the increase in obesity in the US. Access to highly palatable (the scientific term for “tasty”) foods has been considered one of them…but so has stress. Humans in the US have rather high levels of stress compared to other countries (5th out of 151 countries surveyed in 2009), and stress…makes you eat. Specifically, it increases your consumption of tasty foods. It appears to be called “comfort food” for a reason.
(There is an entire site dedicated to this. Now the internet really DOES have everything.)
In fact, comfort food in humans not only improves your mood, it ALSO decreases your cortisol responses to stress. The question is: how does this happen? How exactly does comfort food help your mood and decrease your response to stress? The authors hypothesized that this mechanism might be where taste, stress, and PLEASURE come together.
So the first thing they did was to assess this effect behaviorally. They took a bunch of rats, and gave them access to either sugar water (Koolaid!), saccharin water (so you have a non-caloric sweetener, Sci was VERY pleased they included this), or regular water along with their usual chow. They then put them in restraint stress (which basically involves using either a professional rodent restrainer, or wrapping them up like a little rat burrito for a few minutes), and looked at measures of stress via two hormones, ACTH and corticosterone.
What you can see on the upper left is the total amount of sweet solution compared to water. Rats liked sugar over saccharin, but sipped on both pretty nicely. But the important thing is in panel 3 and 4. In panel 3 you can see the ACTH response to restraint stress in the rats over an hour following the stress. The rats that drank water had a normal stress response, but those who had access to sweet stuff had a LOWER response, which possibly indicates better managed stress.
Panel 4 is a measure of change of CORT, and includes a VERY important control. See the question is: is it the solution? Or is it the SWEET? To figure that out, they have the regular drinking rats above up against rats getting sugar or saccharin solutions by gavage, which is where you drip it directly into the stomach rather than letting the rats TASTE the drink. You can see that the rats with sugar solution showed a big decrease in corticosterone levels, while those with gavage did not. The taste of the sweet is indeed important, being full isn’t going to help.
But is it just sweet stuff? Are there other natural rewards that can reduce rat stress too? To look at this, the authors did the obvious one: rat sex. Some rats got access to a female every day and became some VERY happy rats, while another group of rats got nothing, and another poor group of rats had to get teased by a female nearby, but was unable to actually touch her.
As you can see from panel E, happy rats.
Panel F, though, is the sex, non-sex, and teased rats exposed to restraint stress like in the food group. You can tell that the sex rats had big reductions in corticosterone response to stress, all that sex must be relaxing.
They looked at heart rate and blood pressure in the rats as well, and found that sugar and saccharin consumption improved those measures in response to stress. They even looked at social interaction with other rats (the amount a rat socially interacts with another rat is a measure of anxiety and how stressed out the rat is), and rats with access to tasty drinks interacted with other rats more. They also showed better responses in other anxiety tests like the elevated zero maze (which has a dark section and a light section, rats like the dark, so the more the rat explores the light section, the less nervous it is), and the open field (same principle, rats like corners, how much they explore the center is a measure of how anxious the rat is).
All this behavior is great, but the question is: where is it coming from? What structure is mediating these behaviors? The authors thought it might be the baso-lateral amygdala. The amygdala is a structure in the brain shaped like an almond, and located about here:
(Sci gets a little thrill seeing that she’s the top image result for something like this. It’s like being famous on the internet. Only not really. Source)
The amygdala helps to regulate a lot of emotion related actions. It has a well-known role in fear, and of course it also responses to stress. But it ALSO responds to pleasurable rewards. So the authors took rats with sweet solutions and rats without (they got rid of the saccharin at this point, having proved their point), and then they used a chemical called ibotenate (which always makes me think of IOCAINE) to block out the BLA in half of the rats.
In the normal rats (the first two panels up there) they got normal corticosterone responses to stress, with sugary rats having a reduced corticosterone response (it’s actually pretty small, only 10-20{9f43b4361d9a125bc126dd2a2d1949be02545ec69880430bc4fed2272fd72da3}, but still). The lesioned rats, on the other hand, showed no difference, which shows that you NEED the BLA for sugar to decrease the stress response in rats.
They then looked in sugar treated rats in the BLA for changes in genes, and found a bunch of them that were changed, which they say indicates “synaptic plasticity”. They did find various genes that suggest this (GluR1, CREB, etc), but I wasn’t very impressed. I’d like to see changes in actual signaling and function of the BLA before people start waving their hands and talking about synaptic plasticity.
And guess what? They listened to me! Sort of.
The idea here is that, if sugar intake (the intake of pleasurable rewards) is changing the BLA in terms of function, the rats will show changes in response to stress even AFTER they stop drinking sucrose. And, as you can see up there, they DID. The lower response to stress (a decrease in corticosterone change) remained even 7 days after they stopped feeding them sugar. So it appears we really are seeing some functional changes taking places (though I’d love to see this specifically blocked by BLA lesion at day 3 or something).
Take home message? Eating pleasurable foods (or engaging in pleasurable things like sex) really DOES help your stress. It reduces the biological responses to it, anyway. The changes are small but noticeable. And this appears to involve the BLA.
Sci thought this paper was pretty cool, but there were a couple of little picky things that kind of bugged me:
1) They used restraint stress, and repeated it for the final set of experiments. This isn’t the greatest thing, though restraint stress is really easy, rats DO become tolerant to it over time, so there will be a decrease in response over time. And what if the rats getting sucrose happen to be more tolerant to the stress? While they did control for it, it might have been better to use a stressor where you don’t get tolerant rats, like small footshock.
2) The BLA is a REALLY complicated area of the brain. You get activity there with reward, sure, but you ALSO get activity with stress. While I understand their rationale for wanting to look there (it reacts to reward, and it’s not the nucleus accumbens, which is where everyone else looks), I’d be interested in teasing apart which BLA neurons specifically react to stress or pleasure, and where these circuits lead, and even more, where they come from. You could test excitatory vs inhibitory output, for example, by using techniques like microdialysis to monitor levels of neurochemicals like glutamate (excitatory) or GABA (inhibitory) coming from the BLA to other regions. You could use optogenetics to selectively stimulate excitatory or inhibitory neurons in the BLA, and see what effect this has on stress responses and their reactions to palatable food. I feel like they didn’t really justify their choice of the BLA, and while the lesion proved that the BLA was necessary for the reduced stress response when rats of tasty sweet solutions, it actually didn’t prove that the BLA was SUFFICIENT. So the BLA plays a role…but what role, really?
But there were also a lot of little picky things about this paper that I liked! I liked that they used saccharin, this means you have a non-caloric control. I also like that they used sex. It implies that you can use lots of rewarding behaviors to relieve stress.
But overall, this paper kind of feels like…duh. The entire first half, anyway, has actually been shown in humans (well, ok, I don’t think they’ve had people, say, get stressed and then ejaculate and come back and see if they felt better, but the results from that study I bet would be very similar). The BLA bit is cool, but WHY the BLA? And why didn’t they do more with it? Why just show a bunch of genes and a behavior study?
This paper obviously leaves us with more research in mind. But in the meantime, rest assured, reaching for the pie WILL make you feel at least a little better. Before the guilt sets in.
(Source)
Finally, the last paragraph of this paper has some pure gold in it:
Lastly, although “self-medication” by consumption of highly
palatable, calorically dense comfort foods clearly decreases col-
lective stress responses, reductions can also be achieved by en-
gaging in other naturally rewarding behaviors. The ability to engage
reward systems in the face of stress may be exploited as a means to
diminish the contribution of life stress to the obesity epidemic and
other stress-related disorders.
What does that mean? It means, well, we don’t want to promote the obesity epidemic by encouraging comfort food consumption so…HAVE MORE SEX!
Ulrich-Lai YM, Christiansen AM, Ostrander MM, Jones AA, Jones KR, Choi DC, Krause EG, Evanson NK, Furay AR, Davis JF, Solomon MB, de Kloet AD, Tamashiro KL, Sakai RR, Seeley RJ, Woods SC, & Herman JP (2010). Pleasurable behaviors reduce stress via brain reward pathways. Proceedings of the National Academy of Sciences of the United States of America, 107 (47), 20529-34 PMID: 21059919
